CS 161 - Introduction to Programming with PHP

Computer Organization

• Input unit
• Output unit
• Memory unit
• Arithmetic and logic unit
• Central processing unit
• Secondary storage unit

Sample block diagram from a Supermicro Atom system:

How computers store data, i.e. data types understood by the CPU:

• boolean
• integer
• float

Data types that are understood by PHP:

• Scalar:
  • boolean
  • integer
  • float
  • string
• Compound:
  • array
  • object
• Special:
  • resource
  • NULL

From the PHP documentation:

The type of a variable is usually not set by the programmer; rather, it is decided at runtime by PHP depending on the context in which that variable is used.

Operators (see Chapter 15. Operators)

• Arithmetic
• String
• Comparison
• Assignment

Assignment #2 Due: Friday 24 September

Problem #1:

The following PHP code:

<?php printf("%d\n", 55); printf("%d\n", 055); printf("%d\n", "055"); ?>

Produces the following ouput:

55 45 55

Question: Why? (clue: what does 0x55 print as?)

Problem #2:

Write a program that determines the number of pennies, nickels, dimes, quarters, and dollar bills that are needed to make correct change for a user-entered amount of purchase and payment.

The following code can be used to request input from the user:

$line = trim(fgets(STDIN)); // reads one line from STDIN

Goals of assignment: learn about PHP data types